Voltage regulators of various types for automotive vehicles are well known. In automotive on-board vehicular networks, it is customary to provide an alternating current generator, usually a three-phase generator, which feeds a bridge-type rectifier. A capacitor may be used to filter out ripple in the output voltage. The output voltage is sensed and compared with a reference. In dependence on the comparison, an error signal is obtained which controls the switching state of a switching element, typically a transistor, which connects or disconnects current flow through the field winding of the generator as the voltage varies with respect to the reference. Such a voltage regulator is described, for example, in U.S. Pat. No. 3,571,657, Domann, assigned to the assignee of this application, which, at its input, has an R/C filter network to provide relatively smooth output voltage, that is, to remove ripple from the rectified output of the alternator. The on-board vehicular network, although essentially characterized as a direct-current network, is subject to ripple and voltage peak disturbances, particularly when supplied from an a-c generator. Commutating peaks upon switching-over of the diodes will arise besides the inherent waviness or ripple of the rectified output voltage. Other disturbance voltages and stray peaks may occur caused, for example, directly by the switching of field current to the alternator by the voltage regulator itself. As described in the literature, the voltage peaks are smoothed by the internal resistance of the filter network, that is, of a divider network contained therein, and of the capacitor, which, together, form the R/C network. The amplitudes of the disturbance peaks and needle pulses must be damped in order to prevent effects thereof on the controller. These amplitudes must be substantially below the hysteresis range of the voltage regulator, that is, should be substantially below about 100 mV to 300 mV, considering an overall output voltage of about 12 V nominal. To increase the regulating frequency, and thus improve the dynamic characteristics of the network system, it has been proposed to let commutating peaks pass and not completely filter them out. A compromise must be made between static and dynamic conditions, in which the static conditions determine the control variation with respect to speed and loading. If the ripple on the capacitor increases beyond some predetermined values, a d-c voltage will occur on the base-emitter path of the input transistor to the voltage regulator which affects the sensing operation of the regulator by tending to apply to the regulator a voltage which is lower than that which actually occurs. This results in an undesirably low output voltage from the alternator, arising due to pecularities within the filtering circuit itself.
The circuit described requires capacity values of between 10 nF and 330 nF for the filter capacitor. Capacitors of this type cannot be monolithically integrated in an integrated network which forms the entire voltage regulator; discrete components are required, which increases the overall cost of the regulator since a separate assembly and soldering step is necessary.